When I did mine I took a coffee can full of sheet metal screws and sprayed a can of foamy engine cleaner into the tank, I sealed up all the openings and proceeded to shake and tumble it for about an hour, works best with a little screachin' "honky tonk' playing in the background.
When I dumped out the screws the threads were packed with a rusty clay sort of sludge.
I cleaned the screws off in diesel fuel and returned them to the tank with another can of foamy engine cleaner, a little more "honky tonkin" and I poured them out, not near as much crud but not as clean as I wanted it.
More diesel wash and back into the tank, third time the screws came out as clean as they went in, rinsed the tank, put it in the sun, stuck a hair dryer in it and ran it till it was bone dry.
I didn't seal the tank.
I ran all new lines and fitting, cut and flared my stainless fuel line and put an old style glass bowl filter (the type with the replaceable elements) just ahead of the fuel pump and then put a marine style glass filter (also with a replaceable element) just before the carb.
Nearly 2 years and not a hick up, I expected to have to replace an element early on but it's been fine.
I carry spare elements in my on board tool kit.
YMMV
